This invention relates, in general, to x-ray masks and, more particularly, to x-ray masks having an absorber layer of a small grain size, a low-stress, a low surface roughness, and a low defect density.
Typically, masks used in x-ray lithography have an absorber layer patterned over a substrate layer, wherein the substrate layer is only slightly thicker than the absorber layer. The substrate layer must be sufficiently thin to allow transmission of an x-ray electromagnetic signal through exposed portions of the substrate layer. The absorber layer, on the other hand, must be sufficiently thick to prevent the x-ray electromagnetic signal from penetrating the absorber layer. Because the thickness of the absorber layer is of a same order of magnitude as the substrate layer, a high-stress absorber layer may distort or bend the substrate layer. The distortion caused by the absorber layer may produce overlay errors during x-ray lithography as well as delamination of the absorber layer. Further, the absorber layer may have a high surface roughness or a high defect density thereby adversely affecting mask inspection systems during an inspection of the x-ray masks. In addition, x-ray masks having a large grain size militates against repairs of the x-ray mask by ion etching. Accordingly, it would be advantageous to have a low-stress absorber layer with a small grain size, a low surface roughness, and a low defect density.